Hybrid electromechanical coolant pump

ABSTRACT

The invention relates to a coolant pump having an impeller which is arranged on a pump impeller shaft and having a drive device for the impeller, which drive device has a mechanical drive and an electric-motor drive. The impeller shaft is divided into a driving section and a driven section, and an openable and closable clutch is arranged between the driving section and the driven section. Operation of the coolant pump by either the mechanical drive or the electric-motor drive can be dependent upon a predetermined speed of threshold of rotation of the impeller, and/or upon a predetermined power usage threshold.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. application Ser. No.14/517,914 filed Oct. 19, 2014, which is a continuation-in-part of U.S.application Ser. No. 12/937,746 filed Feb. 6, 2011, which is a U.S.National Phase Entry of PCT/US2009/039112 filed Apr. 1, 2009, whichclaims the benefit of German Patent Application No. 102008019369.0 filedApr. 17, 2008. The entire disclosure of each of the above applicationsis incorporated by reference as if fully set forth in detail herein.

FIELD

The present disclosure relates to coolant pumps which have both amechanical mode of operation and an electric mode of operation, arelated cooling system for an internal combustion engine, and a relatedmethod for operating a cooling system.

BACKGROUND

A coolant pump is known from DE 102 14 637 A1. To be able to realizedifferent driving operation states of a vehicle with such a coolantpump, which has both an electric-motor drive and also a mechanicaldrive, a planetary drive is provided which can be driven by the electricmotor and/or by the mechanical drive. However, such a design is complexwith regard to its mechanical construction and is susceptible tooperation inconsistencies.

It is therefore an object of the present invention to create a coolantpump with a simpler and more reliable design in relation to the priorart and whose operation is efficient and fail-safe.

SUMMARY

In accordance with a preferred embodiment, the pump wheel shaft isdivided into a driving section and a driven section which is separatefrom said driving section. A clutch is arranged between the drivingsection and the driven section and can be opened in order to separatesaid two sections and which can be closed in order to connect the twosections. With this embodiment, the pump wheel can be driven both by anelectric-motor drive and also by a mechanical drive, in each caseindependently.

With the present invention, pumps are provided, such that the mechanicalpump takes over the function of the electric pump in order to boost thepump power for operating conditions for which the electric pump would beinefficient or inadequate. It is also possible to obtain a fail-safefunction for the electric pump, since it can be coupled to themechanical pump if an interruption occurs in the electrical energysupply.

One of the features of the invention is that the operation of a heavytruck engine using a fully variable coolant pump showed that there is aneed for two different flow volumes of coolant fluid. A smaller volumeor amount of coolant flow (i.e. “base flow”) is needed to, for example,avoid hot spots in the engine. A higher volume or amount of coolant flow(i.e. “peak flow”) is needed to, for example, cool the vehicle in fullload conditions.

In principle, the following implementations of the invention arepossible:

(A) Although it is possible to operate both pump types in parallel, itis particularly preferably provided according to the invention that theelectric pump and the mechanical pump be connected in series, with aregulated clutch performing the function of coupling in the mechanicalpump, for example, on the basis of pressure measurements or monitoringof the electrical energy supply.

(B) In the case of a sequential arrangement of the mechanically operatedpump and the electrically operated pump, it is preferable, for bothpumps to use a single pump wheel.

(C) It is also possible according to the invention, as a result of adownsizing of the coolant pump, for said coolant pump to be adapted bothfor the utility vehicle field and also for the passenger vehicle field.In the case of the passenger vehicle field, the warm-up behaviour of theengine can be improved by precise adjustment of the basic coolant flow.

(D) In hybrid vehicles, the invention may also provide a coolant flowwhen the engine is stopped. The coolant flow is required for thefunctioning of the alternator/generator and for the battery. The coolantflow which is required may accordingly be provided by the combinationaccording to the present invention of the electric pump and of themechanically driven pump, without an auxiliary pump being required, asin the prior art.

The invention has numerous benefits and advantages:

(1) A fail-safe design of the entire system, since it is possible, whenthe electric-motor drive is deactivated, for the pump wheel to beactuated solely by the mechanical drive. The decoupling from themechanical drive takes place by means of an actuation of the clutch. Inthe rest position of the clutch, the pump wheel shaft is driven by themechanical drive. In this situation, the clutch could be held in adeactivated state by an electrical mechanism. In the event of anelectrical failure, the clutch will automatically connect the mechanicaldrive to the pump wheel.

(2) Two operating principles for actuating a driving side, wherein thetwo driving sides can be decoupled entirely from the driven side, or thetwo driving sides can be decoupled only individually from the drivenside.

(3) In-line concept for coupling/decoupling with electric-motor drive.The electric-motor drive, which is preferably designed as a brushlessdirect-current (“DC”) motor, is arranged on the driven side of the pumpwheel shaft. The mechanical drive and also the electric-motor drive may,connected by the clutch, be arranged in alignment on the same axis ofthe coolant pump, and drive only a single pump wheel. This is apreferred embodiment.

(4) The concept of the coolant pump according to the invention iscompatible with different coolant pump designs.

(5) If the coolant pump is for an internal combustion engine of apassenger vehicle, the coolant pump according to the invention canprovide hydraulic energy when the internal combustion engine is at astandstill. Post-operation cooling can take place by the main pump wheelby operation of the electric motor.

(6) Sequential operating logic can be obtained with the coolant pumpaccording to the invention, since the pump wheel can be driven either bythe electric motor or by the mechanical drive.

(7) The bearings on the driving side and on the driven side can bearranged in alignment on the same axle.

(8) It is possible to recover electrical energy from the electric-motordrive (generator operation) when the pump wheel is being drivenexclusively by the mechanical drive. From an energy aspect, this isparticularly possible in the overrun mode of the internal combustionengine.

(9) The provision of sufficient cooling power for most operating statesby decoupling the mechanical drive and operation by means of theelectric motor.

(10) As a result of the cubic power characteristic curve of a coolantpump, the electric motor provides a basic volume flow. The maximumdelivery power for maximum cooling power takes place by coupling themechanical drive (without electric-motor pump).

DRAWINGS

Further details, advantages and features of the present invention can begathered from the following description of an exemplary embodiment onthe basis of the drawing, in which:

FIG. 1 shows a sectioned illustration through an embodiment of a coolantpump according to the invention;

FIG. 2 shows a schematic construction of a cooling circuit of aninternal combustion engine having the coolant pump according to theinvention;

FIGS. 3 and 4 show two statistical distribution plots of the pump wheelrotational speed in relation to the engine speed for two transientdriving cycles;

FIG. 5 depicts the power consumption for an embodiment of a coolant pumpaccording to the invention;

FIGS. 6 and 7 show a coolant flow scenario and power consumption,respectfully, for an embodiment of a coolant pump according to theinvention;

FIG. 8 is a cross-sectional view of an embodiment of a coolant pumpaccording to the invention; and

FIG. 9 is a schematic illustration of a cooling circuit of an internalcombustion engine utilizing an embodiment of the coolant pump accordingto the invention.

DETAILED DESCRIPTION

FIG. 1 shows a sectioned illustration through a coolant pump 15according to one embodiment of the invention. The coolant pump 15 has apump wheel (also called an “impeller”) which is arranged on a pump wheelshaft (also called an “impeller shaft”). The pump wheel shaft is dividedinto a driving section 3 and a driven section 11. In the illustratedembodiment, the driving section 3 is formed as a flange-shape structureto which a mechanical drive 1, in the form of a belt pulley in thisexample, is rotationally fixedly connected. In the illustratedembodiment, the arrangement composed of a flange-shape structure 3 and abelt pulley 1 is mounted in a housing 7 by means of a bearing 6.

The mechanical drive 1 may be connected to an internal combustion engineof a motor vehicle, wherein in the illustrated embodiment, it ispossible to use a belt drive. Only the belt pulley 1 is shown in orderto simplify the illustration.

The driven section 11 of the pump wheel (impeller) shaft is mounted inthe housing 7 by means of two bearings 6 and 10, and at its free end 16,supports the pump wheel 13. Here, the free end 16 of the driven section11 is sealed off with respect to the housing 7 by means of a seal 12which is arranged between the pump wheel 13 and the bearing 10.

As is also shown in FIG. 1, the driven section 11 and the drivingsection 3 of the pump wheel shaft can be connected by means of a clutch4 which is arranged between the two sections 3 and 11. The clutch 4 mayfor example be embodied as an electromagnetic clutch with a coil 5.

An electric-motor drive is positioned in the driven section 11 of thepump wheel shaft, which electric-motor drive is arranged, with its rotor9 and a stator 8 which surrounds said rotor 9, in axial alignment withthe mechanical drive 3 on the driven section 11. Here, as shown in FIG.1, the rotor 9 and the stator 8 are positioned in the housing 7.

An optional Hall effect device 14 can be arranged between the rotor 9and the bearing 6.

With this design of the coolant pump 15 according to the invention, itis possible for the pump wheel 13 to be completely separated from themechanical drive 1 by opening the clutch 4. Here, the electric-motordrive, which is preferably embodied as a brushless DC motor, is arrangedon the side of the driven section 11 of the pump wheel shaft. Thisallows the electric motor drive to provide a regulable coolant flow in apredeterminable power range, which is independent of the rotationalspeed of the motor to which the coolant pump 15 is connected, when thedriven section 11 is separated from the driving section 3 by the openedclutch 4.

For this purpose, the rotor 9 of the electric-motor drive is arrangeddirectly on the driven section 11 of the pump wheel shaft, as can beseen from FIG. 1. The stator 8 is integrated, around the same axis ofthe housing 7, in the housing 7 around the rotor 9, as can likewise beseen from FIG. 1.

The electric-motor drive 8, 9 can be regulated by means of a commutatedsignal from an electronic regulating device (not illustrated in any moredetail in FIG. 1). If the driven side 11 is separated from the drivingside 3, the pump wheel 13 can be driven solely by the electric-motordrive. Here, it is provided that sufficient hydraulic output power isprovided in order to provide the required coolant flow or all normaloperating conditions of the engine which is connected to the coolantpump 15. To obtain a maximum available coolant flow, the driven section11 can be connected to the driving section 3 of the pump wheel shaft bymeans of the clutch 4. In this case, the pump wheel 13 is driven solelyby the mechanical drive 1 when the electric motor is deactivated.

FIG. 2 illustrates a schematic construction of a possible coolingcircuit of an internal combustion engine 17 which uses the coolant pump15 according to the invention. In this schematically highly simplifiedillustration, the pump which is driven by an electric motor is denotedby the reference symbol 20 and the mechanically driven pump is denotedby the reference symbol 21. The two pumps, which are arranged in series,may be connected via the clutch 4 to a belt drive 2 and via the beltpulley 1 to the engine 17 for the provision of the required mechanicaldrive energy. In the illustrated embodiment, the coolant circuit alsohas a thermostat 18 and a cooler member 19, such as a radiator, theinteraction of which is shown by the arrows.

The coolant pump can be arranged in a sequential or parallel manner,wherein the electrical pump can be arranged in series or in parallel tothe mechanical driven member. This includes serial/parallel operation inboth mechanical and hydraulic manner (drive side or pump side).

FIGS. 3 and 4 show data of two transient driving cycles evaluated with afully variable pump, with the curves and entries plotted therein. Thegraphs 50 and 60 show two occurrence plots, which show the flowrequirement for two typical drive cycles. The two major occurrences ofbase flow 52 and 62, and peak flow 54 and 64 are depicted.

In the occurrence plot 50, the base flow 52 could be provided by theelectrical pump drive at less than one kW power. The peak flow 54 couldbe provided by the mechanical pump drive at more than one kW power inthe illustrated example.

FIG. 5 illustrates the power considerations of the two major modes for avariable coolant pump. The top graph 70 plots the power consumption ofthe coolant pump, showing the volume flow in liters per minute (1/min)versus the power (in kW). The area 72 is the preferred area for use ofan electrical pump, and the area 74 is the preferred area for use of amechanically driven pump. The borderline for determining the choice ofpump and drive type is shown at 76. The borderline is one kW in theillustrated example.

The bottom graph 80 is the same as occurrence plot 60 in FIG. 4, and isthe basis for the graph 70 and preferred areas 72 and 74, as well asborderline 76. On the basis of graph 80, the borderline for determiningwhether to use mechanical drive or electric drive in this example is atabout 1500 rpm of the impeller.

The power considerations shown in FIGS. 3-5 depict the two major modesfor a variable coolant pump. The base flow provided by the pump can bedelivered by a pump driven by an electric motor, since the powerconsumption is below one kW. The power consumption above one kW isdifficult to be achieved by an electric motor, mainly due to the lack ofelectrical power in common vehicles today. Here, a mechanically drivensystem is preferred. The mechanical drive provides a “boost” when morecooling is needed.

The discussed embodiment above also provides a “failsafe” coolant pump.If the electrical system or power in the vehicle were to fail or stop insome manner, the mechanical drive would take over and the coolant pumpwould be driven by the pulley and mechanical drive. This would allow theoperator of the vehicle to continue to operate the vehicle until theelectrical system failure could be repaired and reactivated.

In addition, the discussed embodiment can continue to deliver coolantthrough the system even when the engine is switched or turned off. Theelectrical drive powered by the battery of the vehicle can continue tooperate the coolant pump and circulate the cooling fluid until theengine and other components are sufficiently cooled. Some vehicles todayrequire use of an auxiliary pump to accomplish this.

Significant benefits and advantages of the invention include thefollowing: (i) Hydraulically parallel or sequential running electric andmechanical pumps with a controlled clutch on the mechanical memberdriven by the backpressure or electrical power of the electric pumpsystem (the clutch is controlled by the electrical power supply of theelectric pump system or by the back pressure of the coolant circuit);and (ii) Mechanically sequential running mechanical and electrical drivesharing one hydraulic member (i.e. impeller).

Beside these features, the inventive coolant pump can be downsized tothe needs for the automotive market segment, where it could improve thewarm-up behavior of the vehicle and engine by exactly applying theneeded base flow with the speed of the electric motor.

In accordance with embodiments of the invention, the coolant pump drivecan be completely decoupled from the FEAD drive side by the clutch, suchas an electromagnetic clutch. The DC motor is integrated in the drivenshaft axle to provide a controllable coolant flow in a definedperformance range completely independent from the engine speed when thedriven axle is decoupled from the drive shaft. For this, the rotor ofthe DC motor is directly mounted on the driven shaft, and is positionedbetween two bearings above and beneath the rotor. The stator is mountedin the coolant pump housing on the same axis.

The DC motor, which preferably is brushless, is controlled by acommutated signal from an electronic control device. If the driven sideis decoupled from the drive side, the impeller can be driven by the DCmotor. This will provide sufficient hydraulic power to meet the requiredcoolant flow for most of the operating conditions of a vehicle. Toachieve the maximum available coolant flow, the driven side is coupledwith the drive side, for example, with an electromagnetic clutch. Theimpeller will then be driven by the FEAD.

As indicated, benefits and features of the embodiments of the inventioninclude: a) failsafe function of the system, due to jointly suppliedvoltage, where the clutch will engage to drive the impeller by thepulley, if the brushless DC motor is powered off; b) inline concept ofOn/Off clutch with an electronic motor in which the DC motor is mountedon the driven side and both of the devices (i.e., the clutch and the DCmotor) are aligned on the same axis and are driving just one impeller;c) hydraulic power can be provided when the engine is not operating; d)sequential operational logic where the impeller can be driven simply byone device (electronic motor or by pulley); e) the bearing of drive sideand driven side are aligned on the same axis; and f) possible electricenergy recovery from the brushless DC motor, if the impeller is drivenby the pulley.

FIGS. 6 and 7 are two additional graphs which illustrate the operationsand benefits of embodiments of the present invention. FIG. 6 depicts thecoolant flow verses engine speed, while FIG. 7 depicts the powerconsumption verses engine speed.

In FIG. 6, which is designated generally by the reference numeral 100,the line 102 depicts the engagement of the electromagnetic clutch. Line104 depicts the amount of 20% of the coolant flow. This amount iscontrolled by the electric DC motor, particularly a brushless DC motor,and also is the maximum amount of flow that the electric motor canproduce. Disengagement of the clutch is represented by the line 106.

With an electric DC motor, only about 5% of the total power is needed toprovide about 20% of the coolant flow.

In FIG. 7, which is designated by the reference numeral 120, the line122 depicts the power consumption when the electromagnetic clutch isengaged. Line 124 depicts the maximum power consumption by the DC motor,which is preferably brushless.

FIG. 8 depicts an embodiment 150 of a dual mode coolant pump inaccordance with the invention. The pump includes a first body member 152which is fixedly connected to a pulley member 154. The body member 152is rotated at input speed by a belt member (not shown) attached to thevehicle engine. This provides the mechanical drive member for rotationof the coolant impeller 156.

Bearing member 158 allows the mechanical drive body member 152 to rotatefreely when it is not needed to drive (rotate) the impeller member 156and provide additional coolant flow to assist in cooling the engine.

The mechanical drive body member is situated inside a housing member160. When the coolant pump 150 is in use, the housing member 160 isattached to the vehicle engine or another component or housing which inturn is attached to the engine and in fluid communication with theengine coolant system.

Impeller shaft member 162 is positioned centrally inside the housing160. The shaft member 162 is fixedly secured at one end 162-A to theimpeller member 156. The other end of the shaft member 162-B is securedto an openable and closeable clutch mechanism 170. The clutch mechanism170 is preferably an electromagnetic clutch mechanism and is operated byelectric coil 180.

The impeller shaft member 162 is rotatably positioned inside the housing160 by a pair of bearing members 172 and 174. An electric motor 190,which preferably is a brushless DC motor, is positioned in the housingand situated between the two bearing members 172, 174. The motor 190includes a stator member 192 and a rotor member 194. The rotor member194 is fixedly secured to the impeller shaft member 162 and rotates withit.

A sealing member 196 is used to isolate the coolant fluid (in which theimpeller 156 is positioned) from the components of the coolant pump 150.In addition, an optional Hall Effect Device (HED) 198 is positioned inthe housing adjacent the rotor member in order to monitor the speed ofrotation of the impeller shaft and provide data to a computer controlsystem, such as, for example, an electronic control unit (ECU). The datagenerated and supplied by the HED as well as other possible datasupplied by other sensors, generally controls the operation of thecoolant pump.

The cooling pump 150 is a dual mode coolant pump for operating andcontrolling the operation of the rotation of the impeller and thus theflow of coolant in the engine and/or vehicle cooling system. Undernormal conditions, the impeller is operated by the electric motor 190.Under these conditions, the electromagnetic clutch mechanism 170 is heldin an open condition by power from the coil member 180. When morecooling is needed, or in a failsafe situation where electric power islost to the coolant pump, the clutch mechanism 170 closes and the shaftmember 162 is rotated by the mechanical drive member 152.

As indicated in the description of FIG. 8, the first body member 152comprises the mechanical drive mechanism for the coolant pump, while theelectric motor 190 comprises the driven drive mechanism for the coolantpump.

FIG. 9 schematically depicts a cooling system 200 for a vehicle engine,as well as a control system 230 for the cooling system. The coolingsystem includes a vehicle engine 202, a thermostat 204, a heat exchanger206, such a as a radiator, and a dual mode coolant pump 208. The coolantpump 208 includes a pulley member 210, a mechanical drive mechanism 212,a clutch mechanism 214, and a DC electric motor 216.

The coolant pump 208 could be, for example, the coolant pump 150discussed above and shown in FIG. 8.

The pulley member 210 is driven by a belt 220 from a pulley member 222attached to and rotated by the vehicle engine 202. Engine coolant flowsfrom the engine 202 through the radiator 206 and then through thecoolant pump 208 before being directed back to the engine.

The control system 230 includes an electronic control unit (ECU) 232which controls the operation of the coolant pump 208. The ECU receivesdata from various sensors, such as one or more temperature sensors 234,which assist in directing the operation of the cooling system. Also,control logic 240 in the coolant pump 208 can be supplied to operate thevarious coolant pump components and mechanisms. The ECU 232 can also bein communication and receive data from one or more other ECUs in theengine and vehicle.

With the present invention, the coolant pump drive can be completelydecoupled from the FEAD drive side by, for example, an electromagneticclutch. A brushless DC motor integrated with the driven shaft member toprovide a controllable coolant flow in a defined performance rangeindependent from the engine speed. For this, the rotor of the brushlessDC motor is directly mounted on the driven shaft member with rollerbearings positioned above and beneath the rotor. The stator is mountedin the coolant pump housing on the same axis.

The brushless DC motor is controlled by a commutated signal from anelectronic control unit. If the driven side is decoupled from the driveside, the impeller is driven by the brushless DC motor. It is designedto provide sufficient hydraulic power to meet the required coolant flowfor the most of the operating conditions of a vehicle. To achieve themaximum available coolant flow, the driven side is coupled with thedrive side, by, for example, an electromagnetic clutch. The impellerwill then be driven by the FEAD.

The present invention provides at least the following: a) a failsafesystem, due to jointly supply voltage, in which the clutch will engageto drive the impeller by the pulley, if the brushless DC motor will bepowered off; b) an inline concept of On/Off clutch with electronic motorin which the brushless DC motor is mounted on the driven side and bothdevices (i.e., the clutch and the brushless DC motor) are aligned on thesame axis and are both positioned operably to drive the same impeller;c) hydraulic power can be provided when the engine is not operating; d)sequential operation logic in which the impeller can be driven just byone device (electronic motor or by pulley); e) bearings on the driveside and the driven side are aligned on the same axis; and f) electricenergy recovery can be provided by the brushless DC motor when theimpeller is driven by the pulley.

While preferred embodiments of the present invention have been shown anddescribed herein, numerous variations and alternative embodiments willoccur to those skilled in the art. Accordingly, it is intended that theinvention is not limited to the preferred embodiments described hereinbut instead limited to the terms of the appended claims. The foregoingdescription of the embodiments has been provided for purposes ofillustration and description. It is not intended to be exhaustive or tolimit the disclosure. Individual elements or features of a particularembodiment are generally not limited to that particular embodiment, but,where applicable, are interchangeable and can be used in a selectedembodiment, even if not specifically shown or described. The same mayalso be varied in many ways. Such variations are not to be regarded as adeparture from the disclosure, and all such modifications are intendedto be included within the scope of the disclosure.

What is claimed is:
 1. A method for operating a cooling system for aninternal combustion engine, the engine having a supply of a coolantliquid and an impeller on an impeller shaft for circulating the coolantliquid in the engine, the method comprising the steps of: providing acoolant pump for rotating the impeller, said coolant pump having both amechanical drive mechanism and an electrical drive mechanism; rotatingthe impeller shaft by said electrical drive mechanism when the speed ofthe impeller is below a predefined speed threshold; and rotating theimpeller shaft by said mechanical drive mechanism when the speed of theimpeller is above the predefined speed threshold.
 2. The method asdescribed in claim 1 wherein said predefined threshold is about 1500rpm.
 3. The method as described in claim 1 wherein the impeller isrotated by said electrical drive mechanism when the power used by theimpeller is less than a predefined power threshold.
 4. The method asdescribed in claim 3 wherein said predetermined power threshold is about1 kW.
 5. The method as described in claim 1 wherein the impeller isrotated by said mechanical drive mechanism when the power used by theimpeller is above a predefined power threshold.
 6. The method asdescribed in claim 5 wherein said predetermined power threshold is about1 kw.
 7. The method as described in claim 1 wherein said electricaldrive mechanism comprises an electric motor.
 8. The method as describedin claim 7 wherein said electric motor is a brushless DC motor.
 9. Themethod as described in claim 1 wherein said electric drive mechanism andsaid mechanical drive mechanism are each operably connected to saidimpeller shaft.
 10. The method as described in claim 9 furthercomprising the steps of: providing a clutch mechanism between saidelectrical drive mechanism and said mechanical drive mechanism; andoperating said clutch mechanism to decouple said mechanical drivemechanism from said impeller shaft when the speed of the impeller isless than a predefined speed threshold.
 11. The method as described inclaim 10 wherein said predefined speed threshold is about 1500 rpm. 12.The method as described in claim 9 further comprising: providing aclutch mechanism between said electrical drive mechanism and saidmechanical drive mechanism; and operating said clutch mechanism tocouple said mechanical drive mechanism to said impeller shaft when thespeed of the impeller is above a predefined speed threshold.
 13. Themethod as described in claim 11 wherein said predefined speed thresholdis about 1500 rpm.
 14. The method as described in claim 1 furthercomprising the step of rotating said impeller shaft by said mechanicaldrive mechanism at any speed of the engine if there is an electricalfailure preventing said electrical drive mechanism from operating. 15.The method as described in claim 9 further comprising the step ofproviding an electromechanical clutch mechanism positioned between saidelectrical drive mechanism and said mechanical drive mechanism.
 16. Themethod as described in claim 9 further comprising the step of providinga hydraulically operated clutch mechanism positioned between saidelectrical drive mechanism and said mechanical drive mechanism.
 17. Themethod as described in claim 16 wherein said hydraulically operatedclutch mechanism is driven by back pressure from the coolant circuit.18. The method as described in claim 16 wherein said hydraulicallyoperated clutch mechanism is driven by electrical power from theelectrical drive mechanism.
 19. The method as described in claim 16further comprising the step of providing a valve and recirculatingsystem for operation of said hydraulically operated clutch mechanism.20. A cooling system for an internal combustion engine, comprising: aninternal combustion engine, said engine comprising fluid for coolingsaid engine; a temperature sensor for determining the temperature ofsaid coolant fluid; a cooler member for dissipating heat from saidcoolant fluid and reducing the temperature of said coolant fluid; acoolant pump assembly for circulating said coolant fluid through saidinternal combustion engine and said cooler member whenever base flow andpeak flow are needed; a control system for operating said coolant pumpassembly based on data provided by said temperature system; said coolantpump comprising a mechanically driven pump mechanism and an electricallydriven pump mechanism arranged in series; said coolant pump furthercomprising a clutch mechanism; and said mechanically driven pumpmechanism being connected by said clutch mechanism in a pulley memberwhich is connected in turn by a belt member to said internal combustionengine and driven at input speed; wherein said coolant pump is operatedby said electrically driven pump mechanism whenever base flow is needed;and wherein said coolant pump is operated by said mechanically drivenpump mechanism only when peak coolant flow is needed.